Hydrogen-containing chlorofluoropropanes such as R225ca and R225cb are expected to be useful as blowing agents, refrigerants or cleaning agents, like conventional chlorofluorocarbons.
Heretofore, a method for synthesizing R225ca and R225cb by the addition reaction of tetrafluoroethylene (hereinafter sometimes referred to simply as 4F) with dichlorofluoromethane (hereinafter sometimes referred to simply as R21) in the presence of an aluminum chloride catalyst, as shown by the following formula. EQU CF.sub.2 =CF.sub.2 (4F)+CHCl.sub.2 F(R21).fwdarw.CF.sub.3 CF.sub.2 CHCl.sub.2 (R225ca)+CClF.sub.2 CF.sub.2 CHClF(R225cb)
[see 1) U.S. Pat. No. 2,462,402 (Du Pont), 1949, 2) D. Coffman, et al., Journal of American Chemical Society, 71,979 (1949), 3) O. Paleta, et al., Collect. Czech. Chem. Commun., 36, 1867 (1971)]
Thereafter, an improved synthesis of R225ca and R225cb employing aluminum chloride or halogenated aluminum oxide alone, as a catalyst in the above reaction, has been proposed.
[see 4) Japanese Unexamined Patent Publication No. 118338/1991 (Daikin), 5) Japanese Unexamined Patent Publication No. 178940/1991 (Daikin), 6) EP-0-421322-A1 (Daikin)]
Methods 1), 2) and 3) employing an aluminum chloride catalyst, have a difficulty that chloroform which forms azeotrope with the desired products, will be formed in a large amount as a by-product, and dichloropentafluoropropane isomers which are hardly separable by a usual method such as distillation because their boiling points are close to those of the desired products, will be formed as by-products. Such isomers include 2,2-dichloro-1,1,1,3,3-pentafluoropropane (hereinafter sometimes referred simply as R225aa) and 2,3-dichloro-1,1,1,2,3-pentafluoropropane (hereinafter sometimes referred to simply as R225ba). Accordingly, they have a drawback that a multi-stage purification process is required in order to obtain highly pure R225ca and R225cb, and it has been desired to suppress the formation of such by-products.
Further, in the improved methods 4), 5) and 6), formation of chloroform is suppressed to some extent, but no improvement has been made with respect to the formation of R225aa and R225ba as by-products.